Avoid redistribute copy if using a single mpi process

[ljgray]

This is relevant because of the check for available memory. If we are on a single node, we don't need to make a new array, so this was effectively limiting users to mpiarrays that were < ~0.4 of the available memory (which could be problematic in a notebook, for example)

[ketiltrout]

I'm assuming everything from line 763 onwards is just left-shifted one indent level. A cursory look seems like that's true.

Otherwise, this looks fine.